The rolling units referred to above, in addition to the rolling mills formed by these rolling units arranged in alignment along a longitudinal rolling axis, are already known from the Applicant's published Italian patent application No. MI92A000917 (corresponding also to European patent application No. 92118389.3); in short, this rolling unit permits the use of at least three driven processing rolls, combining the advantageous effects resulting from this fact with considerable functional flexibility which facilitates the various maintenance and roll-replacement operations. This result is indeed achieved by virtue of the fact that the rolls are mounted on a suitable carrier which can be removed from the structure of the rolling mill, and that the rolls are arranged on pivoting lever arms so that their distance from the rolling axis can be adjusted; in a rolling mill of this type, the stresses generated during the rolling of a pipe fitted on a mandrel are transmitted to the outer load-bearing structure by the elements which support the rolls on each arm, through the device for adjusting the positions of the rolls; the load-bearing structure is constituted, for each rolling unit of the rolling mill, by at least two plate-like elements in the form of circular rings joined together by a series of spacers, these elements rigidly supporting a fixed portion of the device for adjusting each roll.
The outer load-bearing structure is therefore substantially tubular and can effectively absorb the rolling stresses mentioned, precisely by virtue of its closed shape concentric with the rolling axis.
Maintenance of the rolling mill or changing of the rolls, for example, in order to turn them again, are carried out by the removal of all of the roll carriers from the structure of the rolling mill, the carriers being slid axially relative to the structure on suitable guides provided therein and then deposited on a carriage arranged at the output end of the rolling mill for moving the carriers; in a solution of this type, the space downstream of the rolling mill has to be at least equal to the length of the pack of carriers inside the rolling mill to allow the carriers to be positioned on the carriage for moving them. This is not always the case in actual rolling plants since the arrangement (layout) of the various rolling mills (roughing, finishing, etc.) required for carrying out the various stages of the processing of a finished pipe from a billet is such that there is not always sufficient space downstream of a rolling mill such as that considered above for the roll carriers to be removed in accordance with the teaching mentioned.
For this reason, a variant of the rolling unit and of the respective rolling mill just mentioned has therefore been provided and is described and illustrated in published Italian patent application No. MI93A000704 (corresponding also to PCT international application No. EP93/00898) also by the present Applicant. In this variant, the outer structure of the rolling unit is substantially "C"-shaped, that is, open on one side in a radial direction relative to the rolling axis; for rolling-mill maintenance and roll-replacement operations, the carriers on which the rolls are mounted are removed from the load-bearing structure in the aforementioned radial direction by being slid on suitable guides provided in each rolling unit.
This second technical solution is particularly suitable for processing pipes or even rod-shaped bodies and bars, wherein which a mandrel is not used since, because the load-bearing structure of each rolling unit is open laterally, it does not offer the same capacity as the substantially tubular structure described above to contain the rolling stresses mentioned which are transmitted from the mandrel by means of the rolls and the support elements mounted on the pivoting arms.